Well under normal circumstances (unless you have assigned them globally in assign system roles) a user with the role of teacher will be in charge of one course only. They can enrol students although they cannot create accounts from outside Moodle. It is only the site admin who can do that and although it is possible to tweak permissions so that regular users such as teachers can create accounts, is there a very good reason for your wanting to do that?
Roles and permissions
Course Admin
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